Make Protocol.receive_eof idempotent.

This removes the need for keeping track of whether you called it or not,
especially in an asyncio context where it may be called in eof_received
or in connection_lost.

src/websockets/protocol.py

@@ -270,10 +270,11 @@ def receive_eof(self) -> None:
         - You aren't expected to call :meth:`events_received`; it won't return
           any new events.
 
-        Raises:
-            EOFError: If :meth:`receive_eof` was called earlier.
+        :meth:`receive_eof` is idempotent.
 
         """
+        if self.reader.eof:
+            return
         self.reader.feed_eof()
         next(self.parser)
 

tests/test_protocol.py

@@ -1590,18 +1590,14 @@ def test_client_receives_eof_after_eof(self):
         client.receive_data(b"\x88\x00")
         self.assertConnectionClosing(client)
         client.receive_eof()
-        with self.assertRaises(EOFError) as raised:
-            client.receive_eof()
-        self.assertEqual(str(raised.exception), "stream ended")
+        client.receive_eof()  # this is idempotent
 
     def test_server_receives_eof_after_eof(self):
         server = Protocol(SERVER)
         server.receive_data(b"\x88\x80\x3c\x3c\x3c\x3c")
         self.assertConnectionClosing(server)
         server.receive_eof()
-        with self.assertRaises(EOFError) as raised:
-            server.receive_eof()
-        self.assertEqual(str(raised.exception), "stream ended")
+        server.receive_eof()  # this is idempotent
 
 
 class TCPCloseTests(ProtocolTestCase):